The present invention pertains to compositions and methods for plasmid-mediated gene supplementation. The present invention relates to a method of decreasing body fat proportions and increasing lean body mass (“LBM”) in an animal subject. Overall, the embodiments of the invention can be accomplished by delivering a nucleic acid expression construct that encodes a GHRH or functional biological equivalent thereof into a tissue of a subject and allowing expression of the encoded gene in the subject. For example, when such a nucleic acid sequence is delivered into the specific cells of the subject tissue specific constitutive expression is achieved. Furthermore, external regulation of the GHRH or functional biological equivalent thereof gene can be accomplished by utilizing inducible promoters that are regulated by molecular switch molecules, which are given to the subject. The preferred method to deliver the constitutive or inducible nucleic acid encoding sequences of GHRH or the functional biological equivalents thereof is directly into the cells of the subject by the process of in vivo electroporation. In addition, this invention also relates to a method of increasing bone density and improvising the rate of bone healing in an animal subject. More specifically, this invention pertains to both an in vivo and an ex vivo method for delivering a heterologous nucleic acid sequence encoding growth hormone releasing hormone “GHRH” or functional biological equivalent thereof into the cells of the subject and allowing expression of the encoded gene to occur while the modified cells are within the subject. Another embodiment of the present invention relates to regulating the expression of the GHRH using a molecular switch (e.g. mifepistone).
Growth Hormone (“GH”) and Immune Function: The central role of growth hormone (“GH”) in controlling somatic growth in humans and other vertebrates, and the physiologically relevant pathways regulating GH secretion from the pituitary are well known. The GH production pathway is composed of a series of interdependent genes whose products are required for normal growth. The GH pathway genes include: (1) ligands, such as GH and insulin-like growth factor-I (“IGF-I”); (2) transcription factors such as prophet of pit 1, or prop 1, and pit 1: (3) agonists and antagonists, such as growth hormone releasing hormone (“GHRH”) and somatostatin (“SS”), respectively, and (4) receptors, such as GHRH receptor (“GHRH-R”) and the GH receptor (“GH-R”). These genes are expressed in different organs and tissues, including the hypothalamus, pituitary, liver, and bone. Effective and regulated expression of the GH pathway is essential for optimal linear growth, as well as homeostasis of carbohydrate, protein, and fat metabolism GH synthesis and secretion from the anterior pituitary is stimulated by GHRH and inhibited by somatostatin, both hypothalamic hormones. GH increases production of IGF-I, primarily in the liver, and other target organs. IGF-I and GH, in turn, feedback on the hypothalamus and pituitary to inhibit GHRH and GH release. GH elicits both direct and indirect actions on peripheral tissues, the indirect effects being mediated mainly by IGF-I.
The principal feature of GH deficiencies in children is short stature. Similar phenotypes are produced by genetic defects at different points in the GH axis, as well as non-GH-deficient short stature. Non-GH-deficiencies have different etiology, such as: (1) genetic diseases, Turner syndrome, hypochondroplasia; and (2) chronic renal insufficiency. Cases where the GH axis is unaffected (i.e., patients have normal hormones, genes and receptors) account for more than 50% of the total cases of growth retardation. In these cases GHRH and GH therapy has been shown to be effective (Gesundheit and Alexander, 1995).
Reduced GH secretion from the anterior pituitary causes skeletal muscle mass to be lost during aging from 25 years to senescence. The GHRH-GH-IGF-I axis undergoes dramatic changes through aging and in the elderly with decreased GH production rate and GH half-life, decreased IGF-I response to GH and GHRH stimuli leads to loss of skeletal muscle mass (sarcopenia), osteoporosis, and increase in fat and decrease in lean body mass. Previous studies have shown that in elderly the level of GH secretion is significant reduced by 70-80% of teenage level. It has been demonstrated that the development of sarcopenia can be offset by exogenous GH therapy. However, this remains a controversial therapy in the elderly because of its cost and frequent side effects.
The production of recombinant proteins allows a useful tool for the treatment of these conditions. Although GH replacement therapy is widely used in patients with growth deficiencies and provides satisfactory growth, and may have positive psychological effects on the children being treated, this therapy has several disadvantages, including an impractical requirement for frequent administration of GH and undesirable secondary effects.
GH is released in a distinctive pulsatile pattern that has profound importance for its biological activity (Argente et al., 1996). Secretion of GH is stimulated by the natural GH secretagogue, GHRH, and inhibited by somatostatin (SS), and both hypothalamic hormones (Thorner et al., 1990). GH pulses are a result of GHRH secretion that is associated with a diminution or withdrawal of somatostatin secretion. In addition, the pulse generator mechanism is timed by GH-negative feedback The endogenous rhythm of GH secretion becomes entrained to the imposed rhythm of exogenous GH administration. Effective and regulated expression of the GH and insulin-like growth factor I (“IGF-I”) pathway is essential for optimal linear growth, homeostasis of carbohydrate, protein, and fat metabolism, and for providing a positive nitrogen balance (Murray and Shalet, 2000). Numerous studies in humans, sheep or pigs showed that continuous infusion with recombinant GHRH protein restores the normal GH pattern without desensitizing GHRH receptors or depleting GH supplies as this system is capable of feed-back regulation, which is abolished in the GH therapies (Dubreuil et al., 1990a; Vance et al., 1985b; Vance, 1990; Vance et al., 1985a). Thus, GHRH recombinant protein treatment may be more physiologically relevant than GH therapy. However, due to the short half-life of GHRH in vivo, frequent (one to three times per day intravenous, subcutaneous or intranasal (requiring 300-fold higher dose) administrations are necessary (Evans et al., 2001; Thorner et al., 1986). Thus, as a chronic therapy, recombinant GHRH protein administration is not practical.
Extracranially secreted GHRH, as mature peptide or truncated molecules (as seen with pancreatic islet cell tumors and variously located carcinoids) are often biologically active and can even produce acromegaly (Thorner et al., 1984). Administration of recombinant GHRH to GH-deficient children or adult humans augments IGF-I levels, increases GH secretion proportionally to the GHRH dose, yet still invokes a response to bolus doses of GHRH (Bercu et al., 1997). Thus, GHRH administration represents a more physiological alternative of increasing subnormal GH and IGF-I levels (Corpas et al., 1993).
Although GHRH protein therapy entrains and stimulates normal cyclical GH secretion with virtually no side effects, the short half-life of GHRH in vivo requires frequent (one to three times a day) intravenous, subcutaneous or intranasal (requiring 300-fold higher dose) administration. Thus, as a chronic treatment, GHRH administration is not practical. Extracranially secreted GHRH, as processed protein species GHRH(1-40) hydroxy or GHRH(1-44) amide or even as shorter truncated molecules, are biological active (Thorner et al., 1984). It has been reported that a low level of GHRH (100 pg/ml) in the blood supply stimulates GH secretion (Corpas et al., 1993). Direct plasmid DNA gene transfer is currently the basis of many emerging therapy strategies and thus does not require viral genes or lipid particles (Aihara and Miyazaki, 1998; Muramatsu et al., 1998). Skeletal muscle is target tissue, because muscle fiber has a long life span and can be transduced by circular DNA plasmids that express over months or years in an immunocompetent host (Davis et al., 1993; Tripathy et al., 1996). Previous reports demonstrated that human GHRH cDNA could be delivered to muscle by an injectable myogenic expression vector in mice where it transiently stimulated GH secretion to a modes extent over a period of two weeks (Draghia-Akli et al., 1997).
Wild type GHRH has a relatively short half-life in the circulatory system, both in humans (Frohman et al., 1984) and in farm animals. After 60 minutes of incubation m plasma 95% of the GHRH(1-44)NH2 is degraded, while incubation of the shorter (1-40)OH form of the hormone, under similar conditions, shows only a 77% degradation of the peptide after 60 minutes of incubation (Frohman et al., 1989). Incorporation of cDNA coding for a particular protease-resistant GHRH analog in a therapeutic nucleic acid vector results in a molecule with a longer half-life in serum, increased potency, and provides greater GH release in plasmid-injected animals (Draghia-Akli et al., 1999), herein incorporated by reference). Mutagenesis via amino acid replacement of protease sensitive amino acids prolongs the serum half-life of the GHRH molecule. Furthermore, the enhancement of biological activity of GHRH is achieved by using super-active analogs that may increase its binding affinity to specific receptors (Draghia-Akli et al., 1999).
Administering novel GHRH analog proteins (U.S. Pat. Nos. 5,847,066; 5846,936; 5,792,747; 5,776,901; 5,696,089; 5,486,505; 5,137,872; 5,084,442, 5,036,045; 5,023,322; 4,839,344; 4,410,512, RE33,699) or synthetic or naturally occurring peptide fragments of GHRH (U.S. Pat. Nos. 4,833,166; 4,228,158; 4,228,156; 4,226,857; 4,224,316; 4,223,021; 4,223,020; 4,223,019) for the purpose of increasing release of growth hormone have been reported. A GHRH analog containing the following mutations has been reported (U.S. Pat. No. 5,846,936): Tyr at position 1 to His; Ala at position 2 to Val, Leu, or others; Asn at position 8 to Gln, Ser, or Thr, Gly at position 15 to Ala or Leu; Met at position 27 to Nle or Leu; and Ser at position 28 to Asn. The GHRH analog is the subject of U.S. patent application Ser. No. 09/624,268 (now U.S. Pat. No. 6,551,996) (“the '268 patent application”), which teaches application of a GHRH analog containing mutations that improve the ability to elicit the release of growth hormone. In addition, the '268 patent application relates to the treatment of growth deficiencies; the improvement of growth performance; the stimulation of production of growth hormone in an animal at a greater level than that associated with normal growth; and the enhancement of growth utilizing the administration of growth hormone releasing hormone analog and is herein incorporated by reference. In the embodiments of the '268 patent application and specific embodiments herein, the mutated GHRH-encoding molecules lack the Gln, Ser or Thr mutations of the Asn at position 8.
U.S. Pat. No. 5,061,690 is directed toward increasing both birth weight and milk production by supplying to pregnant female mammals an effective amount of human GHRH or one of it analogs for 10-20 days. Application of the analogs lasts only throughout the lactation period. However, multiple administrations are presented, and there is no disclosure regarding administration of the growth hormone releasing hormone (or factor) as a DNA molecule, such as with plasmid mediated supplementation techniques.
U.S. Pat. Nos. 5,134,120 (“the '120 patent”) and 5,292,721 (“the '721 patent”) teach that by deliberately increasing growth hormone in swine during the last 2 weeks of pregnancy through a 3 week lactation resulted in the newborn piglets having marked enhancement of the ability to maintain plasma concentrations of glucose and free fatty acids when fasted after birth. In addition, the '120 and '721 patents teaches that treatment of the sow during lactation results in increased milk fat in the colostrum and an increased milk yield. These effects are important in enhancing survivability of newborn pigs and weight gain prior to weaning. However the '120 and '721 patents provide no teachings regarding administration of the growth hormone releasing hormone as a DNA form
In contrast to protein therapy, nucleic acid transfer delivers polynucleotides to somatic tissue in a manner that, in some embodiments, can correct inborn or acquired deficiencies and imbalances. In other embodiments, vectors such as plasmids are used to supplement basal levels of an expressed endogenous gene product. Gene-based drug delivery offers a number of advantages over the administration of recombinant proteins. These advantages include the conservation of native protein structure, improved biological activity, avoidance of systemic toxicities, and avoidance of infectious and toxic impurities. In addition, nucleic acid transfer, for therapeutic purposes, and plasmid-mediated supplementation of an endogenous gene product allow for prolonged exposure to the protein in the therapeutic range, because the newly secreted protein is present continuously in the blood circulation.
The primary limitation of using recombinant protein is the limited availability of protein after each administration. Plasmid-mediated gene supplementation using injectable DNA plasmid vectors overcomes this, because a single injection into the patient's skeletal muscle permits physiologic expression for extensive periods of time (WO 99/05300 and WO 01/06988). Injection of the vectors promotes the production of enzymes and hormones in animals in a manner that more closely mimics the natural process. Furthermore, among the non-viral techniques for gene transfer in vivo, the direct injection of plasmid DNA into muscle tissue is simple, inexpensive, and safe.
In a plasmid-mediated supplementation expression system, a non-viral nucleic acid vector, such as a plasmid, may comprise a synthetic nucleic acid delivery system in addition to a nucleic acid encoding the GHRH being supplemented. In this way, the risks associated with the use of most viral vectors can be avoided. The non-viral expression vector products generally have low toxicity due to the use of “species-specific” components for nucleic acid delivery, which minimizes the risks of immunogenicity generally associated with viral vectors. Additionally, no integration of plasmid sequences into host chromosomes has been reported in vivo to date, so that this type of plasmid-mediated supplementation of GHRH should neither activate oncogenes nor inactivate tumor suppressor genes. As episomal systems residing outside the chromosomes, plasmids have defined pharmacokinetics and elimination profiles, leading to a finite duration of gene expression in target tissues. Furthermore, the plasmid DNA could be engineered so it would be delivered to the cells in a linear rather than circular form (which would further prevent any genomic integration event); the plasmid could be deleted of the antibiotic resistance gene and bacterial origin of replication, making it completely safe for in vivo therapy.
Efforts have been made to enhance the delivery of plasmid DNA to cells by physical means including electroporation, sonoporation, and pressure. Injection by electroporation involves the application of a pulsed electric field to create transient pores in the cellular membrane without causing permanent damage to the cell. It thereby allows for the introduction of exogenous molecules (Smith and Nordstrom, 2000). By adjusting the electrical pulse generated by an electroporetic system, nucleic acid molecules can travel through passageways or pores in the cell that are created during the procedure. U.S. Pat. No. 5,704,908 describes an electroporation apparatus for delivering molecules to cells at a selected location within a cavity in the body of a patient. These pulse voltage injection devices are also described in U.S. Pat. Nos. 5,439,440 and 5,702,304, and PCT WO 96/12520, 96/12006, 95/19805, and 97/07826.
Recently, significant progress has been obtained using electroporation to enhance plasmid delivery in vivo. Electroporation has been used very successfully to transfect tumor cells after injection of plasmid (Lucas et al., 2002; Matsubara et al., 2001) or to deliver the anti-tumor drug bleomycin to cutaneous and subcutaneous tumors in humans (Gehl et al., 1998; Heller et al., 1996). Electroporation also has been extensively used in mice (Lesbordes et al., 2002; Lucas et al., 2001; Vilquin et al., 2001), rats (Terada et al., 2001; Yasui et al., 2001), and dogs (Fewell et al., 2001) to deliver therapeutic genes that encode for a variety of hormones, cytokines or enzymes. Our previous studies using growth hormone releasing hormone (“GHRH”) showed that plasmid therapy with electroporation is scalable and represents a promising approach to induce production and regulated secretion of proteins in large animals and humans (Draghia-Akli et al., 1999; Draghia-Akli et al., 2002).
The ability of electroporation to enhance plasmid uptake into the skeletal muscle has been well documented, as described above. In addition, plasmid formulated with poly-L-glutamate (“PLG”) or polyvinylpyrolidone (PVP) has been observed to increase plasmid transfection and consequently expression of the desired transgene. The anionic polymer sodium PLG could enhance plasmid uptake at low plasmid concentrations, while reducing any possible tissue damage caused by the procedure. The ability of electroporation to enhance plasmid uptake into the skeletal muscle has been well documented, as previously described. PLG is a stable compound and resistant to relatively high temperatures (Dolnik et al., 1993). PLG has been previously used to increase stability in vaccine preparations (Matsuo et al., 1994) without increasing their immunogenicity. It also has been used as an anti-toxin post-antigen inhalation or exposure to ozone (Fryer and Jacoby, 1993). In addition, plasmid formulated with PLG or polyvinylpyrrolidone (PVP) has been observed to increase gene transfection and consequently gene expression to up to 10 fold in the skeletal muscle of mice, rats and dogs (Fewell et al., 2001; Mumper et al., 1998). PLG has been used to increase stability of anti-cancer drugs (Li et al., 2000) and as “glue” to close wounds or to prevent bleeding from tissues during wound and tissue repair (Otani et al., 1996; Otani et al., 1998).
Although not wanting to be bound by theory, PLG will increase the transfection of the plasmid during the electroporation process, not only by stabilizing the plasmid DNA, and facilitating the intracellular transport through the membrane pores, but also through an active mechanism For example, positively charged surface proteins on the cells could complex the negatively charged PLG linked to plasmid DNA through protein-protein interactions. When an electric field is applied, the surface proteins reverse direction and actively internalize the DNA molecules, process that substantially increases the transfection efficiency.
The use of directly injectable DNA plasmid vectors has been limited in the past. The inefficient DNA uptake into muscle fibers after simple direct injection has led to relatively low expression levels (Prentice et al., 1994; Wells et al., 1997) In addition, the duration of the transgene expression has been short (Wolff et al., 1990). The most successful previous clinical applications have been confined to vaccines (Danko and Wolff, 1994; Tsurumi et al., 1996).
Although there are references in the art directed to electroporation of eukaryotic cells with linear DNA (McNally et al., 1988; Neumann et al., 1982) (Toneguzzo et al., 1988) (Aratani et al., 1992; Nairn et al., 1993; Xie and Tsong, 1993; Yorifuji and Mikawa, 1990), these examples illustrate transfection into cell suspensions, cell cultures, and the like, and the transfected cells are not present in a somatic tissue.
U.S. Pat. No. 4,956,288 is directed to methods for preparing recombinant host cells containing high copy number of a foreign DNA by electroporating a population of cells in the presence of the foreign DNA, culturing the cells, and killing the cells having a low copy number of the foreign DNA.
U.S. Pat. No. 5,874,534 (“the '534 patent”) and U.S. Pat. No. 5,935,934 (“the '934 patent”) describe mutated steroid receptors, methods for their use and a molecular switch for nucleic acid transfer, the entire content of each is hereby incorporated by reference. A molecular switch for regulating expression in nucleic acid transfer and methods of employing the molecular switch in humans, animals, transgenic animals and plants (e.g. GeneSwitch®) are described in the '534 patent and the '934 patent. The molecular switch is described as a method for regulating expression of a heterologous nucleic acid cassette for nucleic acid transfer and is comprised of a modified steroid receptor that includes a natural steroid receptor DNA binding domain attached to a modified ligand binding domain. The modified binding domain usually binds only non-natural ligands, anti-hormones or non-native ligands. One skilled in the art readily recognizes natural ligands do not readily bind the modified ligand-binding domain and consequently have very little, if any, influence on the regulation and/or expression of the gene contained in the nucleic acid cassette.
Thus, the present invention is directed to a novel method of increasing lean body mass, decreasing body fat proportions, increasing bone density, and/or increasing the rate of bone healing in an animal by plasmid-mediated supplementation of GHRH